deeply virtual compton scattering on the neutron at jlab with clas12

2009/12/02– CLAS12 #1 [email protected] B. GenoliniS. Niccolai, IPN Orsay CLAS12 Workshop, Genova, 2/27/08

CLAS12 Central Detector MeetingSaclay, 12/02/09

INFN Frascati, INFN Genova,

IPN Orsay,LPSC Grenoble

SPhN Saclay University of Glasgow

Deeply Virtual Compton Scatteringon the neutron at JLab with CLAS12

e’t

(Q2)

eL*

x+ξ x-ξ

H, H, E, E (x,ξ,t)~~

p p’

2009/12/02– CLAS12 #2 [email protected] B. Genolini

nDVCS with CLAS12: kinematics

ed→e’n(p)

Detected in forward CLAS

Detected inFEC, IC

Not detected

PID (n or ?), p, angles to identify the final state

More than 80% of the neutrons have >40°→ Neutron detector in the CD is needed!

DVCS/Bethe-Heitler event generatorwith Fermi motion, Ee = 11 GeV (Grenoble)

Physics and CLAS12 acceptance cuts applied:

W > 2 GeV2, Q2 >1 GeV2, –t < 1.2 GeV2

5° < e < 40°, 5° < < 40°

<pn>~ 0.4 GeV/c

CD

In the hypothesis of absence of FSI:pμ

p = pμp’ → kinematics are complete

detecting e’, n (p,,),

pμe + pμ

n + pμp = pμ

e′ + pμn′ + pμ

p′ + pμ

FSI effects can be estimated measuringen, ep, edon deuteron in CLAS12(same experiment)


• limited space available (~10 cm thickness)→ limited neutron detection efficiency→ no space for light guides→ compact readout needed• strong magnetic field (~5 T)→ magnetic field insensitive photodetectors (APDs, SiPMs or Micro-channel plate PMTs)

CTOF can also be used for neutron detection Central Tracker can work as a veto for charged particles

CND

CTOF CentralTracker

CND: constraints & design

Detector design under study:scintillator barrel

MC simulations done for: efficiency PID angular resolutions reconstruction algorithms background studies


Simulation of the CND

Geometry:• Simulation done with Gemc (GEANT4)• Includes the full CD• 4 radial layers (or 3, if MCP-PMTs are used)• 30 azimuthal layers (can still be optimized)• each bar is a trapezoid (matches CTOF)• inner r = 28.5 cm, outer R = 38.1 cm

Reconstruction: Good hit: first with Edep > threshold

TOF = (t1+t2)/2, with

t2(1) = tofGEANT+ tsmear+ (l/2 ± z)/veff

tsmear = Gaussian with = 0/√Edep (MeV)

0 = 200 ps·MeV ½ → σ ~ 130 ps for MIPs β = L/T·c, L = √h2+z2 , h = distance betweenvertex and hit position, assuming it at mid-layer θ = acos (z/L), z = ½ veff (t1-t2) Birks effect not included (will be added in Gemc) Cut on TOF>5ns to remove events produced in the magnet and rescattering back in the CND

z

y

x


CND: efficiency, PID, resolution

pn= 0.1 - 1.0 GeV/c= 50°-90°, = 0°

Efficiency: Nrec/Ngen

Nrec= # events with Edep>Ethr.

Efficiency ~ 10-16% for a threshold of 5 MeVand pn = 0.2 - 1 GeV/c

Layer 1 Layer 2

Layer 3 Layer 4

distributions (for each layer) for:• neutrons with pn = 0.4 GeV/c• neutrons with pn = 0.6 GeV/c• neutrons with pn = 1 GeV/c• photons with E = 1 GeV/c (assuming equal yields for n and )

n/ misidentificationfor pn ≥ 1 GeV/c

“Spectator” cut

p/p ~ 5%~ 1.5°


CLAS 12

B. Genolini, T. Nguyen Trung, J. Pouthas

http://ipnweb.in2p3.fr/~detect

Recent measurements at OrsayCEA – Orme des Merisiers

Dec. 2-3, 2009

2009/12/02 – CLAS12 #7 http://ipnweb.in2p3.fr/~detect - B. Genolini

Main issues

• Requested time resolution < 200 ps RMS– Plastic scintillator (best ≈ 2.5 ns

FWHM) Large number of photoelectrons:

> 100

• High magnetic field (5T): no PMT SiPM (MPPC, GAPD, etc.)

APD MCP PMT

• 60-cm long scintillator:– Important light losses

(wrapping, absorption) – Spread of the photon time

distribution

w

h

l = 60 cm

Plastic scintillator (BC408)


The test bench at Orsay

• Scintillator: 60×3×3 cm^3, BC408• Trigger: the time reference is taken from

the thickest scintillator, validated by the coincidence of the two others

• Mobile support to scan the scintillator• Test readout: PMT as the reference, or

SiPM (in a box, for shielding)

Reference readout PMT

(XP20D0) Coincidence scintillators

Trigger scintillator

Test readout:

PMT orSiPM

Mobile support

TestRef

Trig


Results

Single pe

σ2test =1/2 (σ2

test,trig + σ2test,ref − σ2

ref,trig) TestRef

Trig

Test = 1 SiPM Hamamatsu (MPPC 1x1 mm2)• TOF ~ 1.8 ns • rise time ~ 1 ns• nphe ~1

Test = 1 SiPM Hamamatsu (MPPC 3x3mm2)• rise time ~5 ns (> capacitance)• more noise than 1x1 mm2

Test = 1 APD Hamamatsu (10x10 mm2 ) • TOF ~ 1.4 ns• high noise, high rise time

Test = 1 MCP-PMT Photonis/DEP (two MCPs)• TOF ~ 130 ps•tested in B field at Saclay(end of November)

Test = PMT• TOF < 90 ps• nphe ~1600

Thi Nguyen TrungBernard Genolini

S. PisanoJ. Pouthas


Extruded scint. + WLS fiber

• Extruded scintillator made at Triumph

• Wavelength shifting fiber (best results with multi cladding): > 10 pe

• Measurement with a 1×1 m2 MPPC (Hamamatsu SiPM) and a PMT (Photonis XP20D0)

• Time resolution: 1.4 ns RMS

100 ns

Typical signals

PMT averaged signal

20 ns


MCP-PMT

• Double-stage MCP (Photonis-DEP)• Time resolution without magnetic field = 130 ps• Test at CEA under magnetic field: not working at

5 T (amplitude ratio = 10-4)

2-stage MCP

1

10

100

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5

Magnetic field (T)

Am

pli

tud

e (m

V)

2600V

2800V


Simulation of the light collection

Adjusted on thePrototype measurements

w

h

l

Scintillator (BC408)

z

y

x

Readout (MCP PMT)

Readout (MCP PMT)

Prototype (0 layer)

2 layers

Scint. 1

Scint. 2

3 layersScint. 2Scint. 1

Scint. 3

Simulations with Litrani

Pulse shapesRelative light yields

Time resolution along the scintillator length


Issues

1/Can we obtain ~150 ps time resolution give the existing constraints ? (B-field,

space, photodetector lifetime,…) ? (3 MCP-PMTs, APDs, SiPMs,…)

2/If not, can we afford to give up on the TOF measurement ?

TOF measurement has three purposes:

A/ n/ separation

B/ pn measurement

C/ measurement

Energy deposition profile (1cm2 scintillator trapezoids) ?

Preshower ? Pulse shape analysis ?

Could measuring only (pe,e,e), (p,), (n,n)

be enough ?

Additional segmentation in

3/Measuring the recoil proton instead ?

deeply virtual compton scattering on the neutron at jlab with clas12

Documents